Altered Leaf Structure and Function in Triazine-Resistant Common Groundsel (Senecio vulgaris)

Anatomical and physiological characteristics of leaves of triazinesusceptible and -resistant biotypes of common groundsel (Senecio vulgaris L.) were studied in order to explain the differences in light-saturated photosynthetic rates previously reported. Leaves were of uniform leaf plastochron index from greenhouse-grown plants. Susceptible plants had greater leaf fresh and dry weights and leaf areas, while resistant plants had greater specific leaf mass (mg fresh weight/cm²). Susceptible plants had greater amounts of total chlorophyll per unit leaf weight and a higher chlorophyll a/b ratio. Soluble protein in leaves was higher in susceptible chloroplasts on a weight and area basis, but similar to resistant chloroplasts on a unit chlorophyll basis. Activity of ribulose 1,5-bisphosphate carboxylase was higher in resistant plants on a fresh weight, leaf area, and milligram chlorophyll basis. Stomatal frequency, length, and arrangement were similar between biotypes, as were transpiration and conductance. Resistant leaves had less air space (v/v), more cells in palisade and spongy mesophyll, and a greater volume of palisade tissue than spongy, when compared to susceptible leaves. Differences in leaf structure and function between biotypes are probably due to a complex of developmental adaptations which may be only indirectly related to modified photosystem II in resistant plants. These results indicate that the consistently lower rates of net photosynthesis and yield in resistant plants cannot be explained solely on the basis of these leaf characteristics. Several possible mechanisms to account for reduced productivity are suggested.     

The Effects of Temperature on the Respiratory Responses of Groundsel (Senecio vulgaris) to Infection by Rust (Puccinia lagenophorae)

Groundsel (Senecio vulgaris) was grown in either a warm (20°C) or a cool (8°C) controlled environment and infected with Puccinia lagenophorae. Dark respiration, measured over the range 6 to 18°C, was higher in leaves of healthy plants grown under low temperatures than in those of plants grown under high temperatures. Infection increased the rates of dark respiration in the region of sporulating lesions in both sets of plants, but the greater increase in plants grown under warm conditions resulted in both sets having similar respiration rates across the range 6 to 18°C. The conclusion that the magnitude of the respiratory increase following rust infection depends upon the conditions under which plants were grown is supported by literature on other rust diseases and has implications for the utilization of carbohydrate reserves and the survival of both rust and host populations over winter.     

基于同源搜索的甜菜miRNAs计算识别

microRNAs（miRNAs）是一类调控真核基因转录后表达的非编码小分子RNA,在调节生物功能方面起着重要的作用,采用基于同源搜索的计算方法预测未知miRNAs是当前发现和鉴定miRNAs的有效策略之一,甜菜是一种重要的制糖工业原料,其miRNAs的识别尚未见报道,本文根据公共数据库中的甜菜EST和GSS信息,采用Blastn同源搜索技术,预测了甜菜（Beta vulgaris）中的候选miRNAs。通过分析候选miRNAs的序列特征,包括碱基错配、二级结构、（A＋U）含量、能量水平等,从中获得了54个miPRNAs,其中,3个miRNAs与miRBase中已知的其他物种高度相似的序列,其余可能为新miRNAs。     

Morphogenetic Responses to Gibberellic Acid of a Radiation-induced Mutant Dwarf in Groundsel, Senecio vulgaris L.

A dwarf mutant of Senecio vulgaris L. induced by gamma radiation,which differs from the wild-type by a single recessive gene,grew as tall as the wild-type plant, and almost five times astall as dwarf control plants when treated at weekly intervalsfrom the seedling stage with 10 p.p.m. gibberellic acid. Thewild-type groundsel responded only slightly to similar treatment.Some evidence was obtained that the response to GA was relativilygreater when plants were grown during the late autumn. Dwarfnessin the mutant is due to fewer as well as to shorter internodes;the rate of leaf initiation is reduced, but the onset of thereproductive phase and the duration of the life-cycle are notaffected by the mutation. Gibberellic acid leads to a conspicuouselongation of the internodes intreated dwarf plants, but notalways to a significant increase in their number. An increasein the dry weight of treated plants was observed, and this wasshown to be due to an increase in photosynthetic area and notto increased photosynthetic efficiency. Comparative observationsof shoot morphogenesis in wild-type and dwarf groundsel. andin dwarf treated with gibberellic acid, have shown that thetype of shoot development induced by gibberellic acid in dwarfplants does not correspond exactly to the normal mode of developmentin wild-type plants. Increased mitotic activity in the subapicaltissue of the mutant following gibberellic acid treatment resultedin greater and earlier elongation of the internodes. However,the typical form and dimensions of the wild-type plant werenot wholly restored.     

The Effects of Infection by Rust (Puccinia lagenophorae Cooke) on the Growth of Groundsel (Senecio vulgaris L.) Cultivated under a Range of Nutrient Concentrations

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae Cooke, was grown at a rangeof nutrient concentrations in sand culture. There were statisticallysignificant interactions between the effects of infection andnutrient supply upon the dry weights of stems, leaves, rootsand reproductive tissues, leaf area and cumulative capitulumproduction. This interaction occurred since infection causedsignificant inhibitions of growth only at moderate or high nutrientconcentrations. At low concentrations rusted plants were similarto or slightly larger than controls. Both in controls and rustedplants root: shoot ratios increased as nutrient supply declined.The ratio of root: shoot dry weight was consistently reducedby infection whilst root length: leaf area ratio was relativelyunchanged. More detailed investigations confirmed that infection had littleeffect on plant growth under nutrient deficient conditions despitesuppression of the host's ability to increase root: shoot ratiosin response to nutrient stress. This reflected the inhibitionof relative growth rates in rusted plants at high but not lownutrient concentrations, which in turn reflected reduced netassimilation rates (NAR). Increases in leaf-area ratio (LAR)often ameliorated the decline in NAR in rusted plants. Senecio vulgaris L., Puccinia lagenophorae Cooke, nutrient deficiency, growth, root: shoot ratio     

The Effects of Nutrient Deficiency and Rust Infection on the Relationship Between Root Dry Weight and Length in Groundsel (Senecio vulgaris L.)

Groundsel (Senecio vulgaris L.) was grown in sand culture ata range of nutrient concentrations. Except when nutrient deficiencywas severe, infection by the rust fungus Puccinia lagenophoraeCooke substantially reduced root dry weight but had little effecton root length. Thus, specific root length (SRL, cm root mg^–1d. wt) was significantly increased in rust-infected plants.The inhibition of root dry weight caused by rust infection wasmost pronounced late in development, especially after floweringwhen, in control plants, root elongation but not dry weightaccumulation ceased. In rusted plants, and in all plants subjectedto severe nutrient deficiency, dry weight accumulation in theroots ceased concurrently with root elongation. Late in developmentat high nutrient concentration adventitious roots with low SRLswere produced. However, infection did not modify the productionof such roots and increases in SRL could not be attributed tochanges in any single type of root. There was an inverse relationship between SRL and root diameter.This relationship was unaffected by rust infection whilst nutrientdeficiency changed only its intercept: at a given SRL rootsof nutrient stressed plants were thinner than those of plantswith adequate nutrient supply. Thus, the smaller diameter ofroots of nutrient-stressed plants occurred independently ofmeasured changes in SRL but, in the absence of nutrient stress,the decrease in root diameter caused by rust was closely relatedto increases in SRL. Changes in the root: length relationships in rusted plants mayhave important implications for root activity in the field.In view of the reported changes in SRL, inhibition of root growthin terms of dry weight may be a poor indicator of potentialchanges in activity. Senecio vulgaris, rust infection, nutrient deficiency, root weight: length ratio, root diameter     

Survivorship and fecundity of the radiate and non-radiate morphs of Groundsel,Senecio vulgaris L., raised in pure stand and mixture

British populations of Senecio vulgaris frequently contain two common capitulum morphs (radiate and non-radiate) and one rare intermediate morph. The radiate morph shows a higher maternal rate of intermorph outcrossing than the non-radiate morph and due to the ‘cost of outcrossing’ should decline in frequency, ultimately to be lost from a population. To determine whether the radiate morph exhibits some inherent advantage in fitness to offset the ‘cost of outcrossing’, a comparison was made of the survivorship and fecundity of the radiate and non-radiate morphs raised in pure stands and 1 : 1 mixture at three planting dates (autumn 1983, and spring and autumn 1984). Plants in stands established in spring 1984 were harvested in late August 1984, while plants in stands established in autumn overwintered before being harvested the following summer. In spring planted stands, the two morphs exhibited equivalent survivorships, while the fecundity of the non-radiate morph tended to be greater than the radiate morph. In autumn planted stands, survivorship and Net Reproductive Output (survivorship × fecundity) of the non-radiate morph was greater than that of the radiate morph in mixture, and also in pure stands established in 1983. In no instance was the Net Reproductive Output of either morph significantly greater in mixture than in pure stand. Density had a contrasting effect on morph survivorship and fecundity in the spring and autumn 1984 planted stands. Whereas, in spring stands, fecundity was subject to compensating density dependent regulation while survivorship was density independent, the opposite trend was observed in autumn planted stands. It is concluded that under the conditions of the experiments, the radiate morph exhibited no fitness advantage which might offset the inherent disadvantage it suffers in natural polymorphic populations due to the ‘cost of outcrossing’.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations II. Uptake of N, P and K and Shoot-Root Interactions

Groundsel (Senecio vulgaris), healthy or infected with rust,Puccinia lagenophorae, was grown at a range of nutrient concentrationsin sand culture. Specific absorption rates calculated on thebasis of root dry weight (SAR_W) were greater in rusted thancontrol groundsel for nitrogen, potassium and phosphorus. Whilethe magnitudes of these stimulations varied, they occurred acrossthe whole range of nutrient concentrations. By contrast, specificabsorption rate on the basis of root length (SAR_L) were littlechanged by rust at any external nutrient concentration; SAR_Lfor phosphate and potassium were slightly reduced when nutrientswere freely available. Water flux per unit dry root weight and length was stimulatedby rust because transpiration per unit leaf area was more rapidin infected plants after fungal sporulation. However, water-fluxand the rate of uptake of nutrients were correlated only whenexpressed on the basis of root weight and increased transpirationdid not appear to be the mechanism underlying increased rootactivity. Rather, increased SAR_W for N, P and K could very largelybe attributed to increased shoot demand per unit root, whichresulted from the higher shoot: root (S: R) ratios of infectedindividuals. Changes in S: R accounted for 92, 81 and 57% oftotal variation in SAR_W for K, P and N respectively. Greatervalues for SAR_W were possible because specific root length (SRL)increased, producing more functional root per unit root weight.The lack of stimulation in SAR_L in response to rust could beexplained since the higher SRL of infected plants resulted instable values of shoot weight per unit root length, i.e. shootdemand was not increased by infection on this basis. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient uptake, water uptake, shoot: root interactions     

Computational identification of miRNAs,their targets and functions in three‐spined stickleback (Gasterosteus aculeatus)

An intriguing question in biology is how the evolution of gene regulation is shaped by natural selection in natural populations. Among the many known regulatory mechanisms, regulation of gene expression by microRNAs (miRNAs) is of critical importance. However, our understanding of their evolution in natural populations is limited. Studying the role of miRNAs in three‐spined stickleback, an important natural model for speciation research, may provide new insights into adaptive polymorphisms. However, lack of annotation of miRNA genes in its genome is a bottleneck. To fill this research gap, we used the genome of three‐spined stickleback to predict miRNAs and their targets. We predicted 1486 mature miRNAs using the homology‐based miRNA prediction approach. We then performed functional annotation and enrichment analysis of these targets, which identified over‐represented motifs. Further, a database resource (GAmiRdb) has been developed for dynamically searching miRNAs and their targets exclusively in three‐spined stickleback. Finally, the database was used in two case studies focusing on freshwater adaptation in natural populations. In the first study, we found 44 genomic regions overlapping with predicted miRNA targets. In the second study, we identified two SNPs altering the MRE seed site of sperm‐specific glyceraldehyde‐3‐phosphate gene. These findings highlight the importance of the GAmiRdb knowledge base in understanding adaptive evolution.     

Adaptation of Senecio vulgaris (Asteraceae) to ruderal and agricultural habitats

Adaptation of the annual plant Senecio vulgaris to ruderal and agricultural habitats was investigated. We expected S. vulgaris to be adapted to the agricultural habitat through nutrient-specific differentiation of relatively few genotypes responding to the generally high homogenous nutrient levels at the agricultural habitat caused by constant fertilization. To assess adaptation of S. vulgaris, vegetative and reproductive responses of seed families from various populations of agricultural and ruderal habitats, grown in the greenhouse at high and low nutrient levels, were compared. Data were analyzed with a three-level nested ANOVA based on the levels habitat, population, and family. A significant habitat effect indicated that S. vulgaris from ruderal and agricultural habitats were genetically different with plants from the agricultural habitat having larger leaves and a higher reproduction. A significant habitat by nutrient effect showed a stronger response of reproduction to nutrients at the agricultural habitat, suggesting that genetic differentiation among habitats is nutrient-specific. Contrary to expectations, only the agricultural habitat showed genetic diversity of S. vulgaris. Results suggest that nutrient levels at the agricultural habitat are more heterogeneous as generally proposed leading to a relatively high genetic variation.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

Changes in Tissue Freezing in Senecio vulgaris infected by Rust (Puccinia lagenophorae)

Freezing of healthy and rust (Puccinia lagenophorae) infectedleaves of Senecio vulgaris was compared calorimetrically bythermal analysis. In fully expanded leaves the threshold freezingtemperature was in the range –6.8 to –8.4 °Cin controls but –3.0 to –5.1 °C in leaves withsporulating rust sori. Comparable values in expanding leaveswere –5.0 to –8.9 °C and –3.9 to –6.7°C for healthy and rusted tissues, respectively. The bulktissue freezing point was between –1.0 and –4.0°C in both fully expanded and expanding healthy leaves,and was increased by infection by between +0.2 and 2.5 °C.Whereas healthy leaves supercooled by 3.1–5.8 °C,rusted leaves supercooled by only 1.8–4.9 °C Supercoolingof control leaves was reduced by dusting with aeciospores, particularlywhen leaves were wounded to simulate the rupture of the surfacecaused by sporulation, but wounding alone had no significanteffect. Supercooling of distilled water was also significantlyreduced by aeciospores, suspended at a concentration of 10⁵spores ml^–1. It is concluded that rust-induced changes in leaf freezing inS. vulgaris grown in controlled environments were due to anincrease in the number of sites for ice nucleation, caused bythe presence of the aeciospores, and increased penetration ofice into internal tissues, resulting from damage to the cuticleand epidermis. Although data for frost resistance obtained inthe growth-room are similar to previous field observations,the role of the above mechanisms under field conditions remainsunproven. Senecio vulgaris (groundsel), Puccinia lagenophorae (rust), low temperature, freezing resistance     

Species identification of the medicinal plant Tulipa edulis (Liliaceae) by DNA barcode marker

Tulipa edulis (Liliaceae) is the botanical origin of the traditional Chinese medicine (TCM) “Guangcigu”. Due to overexploitation that induced a decline in natural sources, many dried bulbs from other species of Tulipa have been used, adulterating the medicine in recent years. This practice may cause a series of inconsistent therapeutic effects and quality control problems in the herbal medicine industry. Hence, three DNA regions (matK, psbA-trnH and rbcL) were evaluated as barcodes for identifying T. edulis and its adulterants. All candidate DNA barcodes were successfully amplified from leaf samples. Based on the sequence divergences, rbcL and psbA-trnH can assign T. edulis and its adulterants to the correct genus, while matK can accurately differentiate T. edulis and its adulterants. Thus, at the DNA level, the matK intergenic region is a more suitable, accurate and applicable identification of T. edulis and its adulterants than rbcL and psbA-trnH.     

The anthers of Senecio vulgaris (Asteraceae): saltatory evolution caught in the act

Anthers of the common annual weed, Senecio vulgaris, show an incomplete development of the two adaxial pollen sacs (microsporangia, MS). One or both adaxial MS can be missing, or they are replaced by sterile lobes. The reduction is stronger in the derived subspecies, S. vulgaris var. vulgaris than in the ancestral subspecies, S. vulgaris ssp. denticulatus. This character in S. vulgaris differs from the usual complete reduction of adaxial MS in other, independent instances of disporangiate anthers in the Asteraceae. It corresponds to the transition phenotypes associated with various recombinant genotypes derived from artificial crosses between tetrasporangiate (4 MS) and disporangiate (2 MS) species in the Asteracean genus Microseris. Senecio vulgaris could be a rare natural instance of homozygosity for a major gene permitting reduction of the adaxial MS in which the expression of the reduced phenotype is determined by different numbers of modifiers in the two subspecies.     

DNA barcoding of medicinal plant material for identification

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Computational identification of putative miRNAs and their target genes in pathogenic amoeba Naegleria fowleri

Naegleria fowleri is a parasitic unicellular free living eukaryotic amoeba. The parasite spreads through contaminated water andcauses primary amoebic meningoencephalitis (PAM). Therefore, it is of interest to understand its molecular pathogenesis. Hence,we analyzed the parasite genome for miRNAs (microRNAs) that are non-coding, single stranded RNA molecules. We identified245 miRNAs using computational methods in N. fowleri, of which five miRNAs are conserved. The predicted miRNA targets wereanalyzed by using miRanda (software) and further studied the functions by subsequently annotating using AmiGo (a geneontology web tool).